Passing a stream or ribbon of molten glass through a nip gap formed by a pair of rollers is one of the oldest methods of producing sheet glass. The thickness of the rolled sheet glass is determined by the nip gap, which means that any variations in the width of the nip gap as the rollers rotate will be transferred to the thickness of the rolled sheet glass. Typically, collars mounted in recesses in the rollers are used to set the nip gap between the rollers. The collars on one roller are pressed against the collars on the other roller to set the nip gap. Variability of the nip gap is influenced by the dimensional accuracy of the rollers, collars, and recesses in which the collars are mounted.